Offset electrophotography



Dec. 31, 1963 E. K. KAPRELIAN 3,115,814

OFFSET ELECTROPHOTOGRAPHY Original Filed Dec. 6, 1955 2 Sheets-Sheet 1 IN V EN TOR Dec. 31, 1963 E. K. KAPRELIAN 3,115,814

OFFSET ELECTROPHOTOGRAPHY Original Filed Dec. 6, 1955 2 Sheets-Sheet 2 IN V ENTOR HG 4 WHI=Z MM United States Patent Ofi ice Patented Dec. 31, ltifiii 3,115,814 OFFSET ELECTROPHOTOGRAPHY Edward K. Kapreiian, 29 River-edge Road, New Shrewsbury, NJ.

Original application Dec. 6, 1955, Ser. No. 551,289, new Patent No. 3,051,568, dated Aug. 28, 11962. Divided and this application .luly 9, 1962, Ser. No. 2ll8,359

1 Ciahn. (Cl. 955-437) This invention relates to electrophotography of the type whereby photographs are produced by the action of light on an electrostatically charged photoconductive insulator; this application is a division of application Ser. No. 551,289 filed Dec. 6, 1955, now Patent No. 3,051,568.

The use of such certain photoconductive insulators as selenium, anthracene, zinc oxide, etc. to produce photographs through the practice of such methods of electrophotography as xerography and Electrofax is well known. In the usual method a thin layer of the photoconductive insulator is given an electrostatic charge and the charged plate or sheet is exposed in a camera or printer. Where-- ever the light strikes the surface the charge leaks off in proportion to the amount of light, with the result that a latent image of varying electrostatic potentials is pro duccd on the plate surface. This latent image is next developed through the use of a finely divided, usually pigmented, material which by selective attraction to the plate produces a visible powder image which, in turn, may be transferred to another surface, or fixed on the plate or sheet by various means well known in the art.

One typical method of electrostatic electrophotography utilizes a rotating drum which, as it rotates, receives the following treatment at successive stations:

(1) The photoconductive insulator surface, usually selenium, receives an electrostatic charge.

(2) The charged surface receives light in the pattern of the desired image, and the charge leaks off selectively to produce an electrostatic latent image.

(3) The electrostatic latent image is developed into visible form by the application of a suitable finely di vided powder.

(4) The powder is transferred to a paper or similar base.

(5) The transferred powder image is fixed through the application of a heat or a solvent.

(6) The plate surface is cleaned preparatory to repetition of the cycle.

By contrast with this method the present invention employs an intermediate step of transferring the electrostatic image to an insulating surface on which the image is developed. The developed image is then fixed on this insulating surface, or it may be transferred to another surface and fixed there.

One of the objects of this invention is to permit the use of a smaller photoconductive insulator surface for a given capacity or speed of operation; or conversely to increase the capacity or speed of operation for a given size of photoconductive insulator surface.

Another object is to prolong the useful life of photoconductive insulator surfaces by eliminating the deteriorating effect of developing and cleaning operations.

Still another object is to provide such gentle action on the surface during cycling as to permit the use of softer, frailer photoconductive insulator layers which cannot withstand repeated developing and cleaning operations.

Still another object is to permit simple and direct control of image contrast.

Still another object is to permit ready reversal of the final image, ie from a positive to a negative.

Still another object is to permit the steps of powder transfer and plate cleaning, usually performed in the dark in drum machines, to occur in light where observation, servicing and adjustment is readily accomplished.

Still another object is to improve the quaiity of line images to permit the production of half tone images.

These and other objects of the invention can be determined from the specification and drawings in which:

FIG. 1 shows the action of transferring a charge to an uncharged surface,

FIG. 2 shows the action of transferring a charge to a surface of opposite charge,

PEG. 3 shows the action of transferring a charge to a surface of similar charge,

FIG. 4 shows in schematic elevation an electrophotographic printer employing a charge transfer belt for producing multiple copies,

FIG. 5 shows in schematic elevation an electrophotographic printer employing a charge transfer belt for pro ducing reproductions of opaque copy,

FIG. 6 shows in schematic elevation an electrophotographic printer in which the latent electrophotographic image is transferred directly to the paper on which the copy is to be made,

FIG. 7 shows a printer in which each unit of opaque copy is reproduced on an individual sheet of paper through direct image charge transfer,

FIG. 8 shows in cross section one form of image transer belt which can be used,

FIG. 9 shows in cross section another form of image transfer belt which can be used,

FIG. 10 shows in cross section still another form of image transfer belt which can be used,

FIG. 11 shows in cross section still another form of image transfer belt which can be used.

The action of image charge transfer is shown in PEG. 1 in which an electrophotographic drum it} having the usual photoconductive insulator coating of selenium or other suitable material carries a positive image charge, or electrostatic latent image, consisting of alternately charged and uncharged areas 12 and M respectively as indicated by the plus symbols and the zeros. Transfer of the image charge to an electrostatically neutral insulating surface 16 takes place at the point of contact it the drum and surface moving in the direction of the arrows. After transfer, the original image on the drum and the transferred image on the sheet have the initial charge pattern, as shown at Ztl and 22, respectively.

In FIG. 2 there is shown the corresponding action when the insulating sheet 16 receives a negative charge 26 from corona wires 24 prior to transfer at point 28. The charges resulting on the drum and sheet after transfer are shown at 3% and 32, respectively. In addition to sharing the charge it is clear that reversal has occurred.

In FIG. 3 the plate :16 is positively charged by wires 24 as at 34. After transfer at point of contact 36 the charges finally remaining on the drum and plate at 38 and 4%, respectively, show that the charge has again been shared. Obviously, corresponding transfers of opposite sign would result if the drum were initially given a negatively charged electrostatic image instead of one of positive sign. It is also possible to produce a charge on the insulating transfer belt or sheet by induction rather than by contact. In this case the belt or sheet would be brought close to the drum, and the back of the belt or sheet grounded to induce a charge on the belt in a manner well known in electrostatics.

FIG. 4 shows an electrostatic latent image transfer printer for producing multiple copies from transparent originals. In this modification an electrophotographic drum 42 receives, through slit 44 and projection lens to, an image of film 48. A suitable light source is provided above the film by head 50. The film is driven by a sprocket 52 in the direction shown through suitable gearing, or equivalent, at the proper speed relative to that of the drum to insure that the image is stationary on the drum, i.e. at a speed ratio equal to that of the conjugate foci the lens.

Drum 42, rotating in the direction shown, receives a charge at charging station 54 and is exposed as it passes slit It contacts an endless belt 56 at 58 where the electrostatic ima e or image charge is transferre to the belt in the manner shown in FlGS. 1 to 3. The belt, rotating in the direction shown may or may not receive a iodifying charge from electrodes on for the purpose of controlling image contrast or otherwise modiiying the image. A developing station 62 of the type which cascades a carrier type developer over the drum produces a powder image which is then transferred, at transfer station s4, to a suitable base, such as paper from a roll 66. This transfer station includes a first point 68 at which an initial heavy transfer of powder occurs and a second point 7% at which all powder in excess of that necessary to form an acceptable image is returned to the belt electrostatically in a manner already known in the art. to image on the paper is permanently fused to the base at a fixing station 72. The belt progresses to succeeding transfer stations '74-, 7s and 7% and is thereafter cleaned at a cleaning station for the purpose of removing residual powder. The belt continues past a chmging station 82 and the cycle is repeated. Belt 56 is made of a suitable flexible dielectric material such as rubber or some synthetic resin as polyethylene or various polyesters and vinyls. While shown as a belt for convenience the transfor surface may be in the form of a cylinder, for example, if such shape is desirable for the geometry of the printing machine. The surface of the belt may be smooth or provided with a texture as described below.

HG. shows a charge transfer printer for opaque copy. A conveying belt 90 carries the sheets 92 of material to be copied past suitable light sources such as mercury vapor tubes 94 and against an enveloping belt 96 which reverses the direction of the copy material and guides it to a receiving tray 98. Belt 9% is suitably driven through gears or toothed belt lt ll from a speed change transmission 102. The transmission is in turn connected to drive electrophotographic drum 104 through similar positive drive means ill-6. The transmission ratio can be changed to accommodate various magnifications or reduction.

Copy )2r is imaged by lens 107 past slit 1% onto the drum. A mirror lltl may be employed to fold the path for reasons of compactness and also for the purpose of producing rectified (unreversed) prints. The usual charging station 1112 is associated with the drum at a point near the slit. After exposure at the slit the charge is transferred to a moving belt 114 and the transferred electrostatic image is developed at station 116. Two vibrating rollers 118 in contact with the belt and driven by suitable motors or vibrators 12%) remove excess or unwanted powder from the belt prior to reaching transfer station 122 where the powder image is transferred to paper from roll 124. The printed copies are fixed at station 126 and are wound on reel 12%. The belt is charged at charging station 130 to control contrast or type of the final image or may be left uncharged as desired.

In FIG. 6 the latent electrostatic image is transferred directly to the paper base. In this modification a projection head generally indicated at 140 moves the film synchronously with an electrophotographic drum 142 in a manner similar to that shown and described in connection with FIG. 4. After exposure is accomplished at slit 1-44, the drum transfers the image charge to a sheet of paper or other suitable material from a roll 146 at a transfer station 143. The paper is carried on a belt supported by pulleys 1 .52. The paper enters a developing station 154 which may employ cascading carrier beads or a powder cloud and separates from the belt 150 at the bottom pulley 1152.. The image is fixed at station 1156 and passes through rollers to a take-up reel 160.

FIG. 7 shows a printer which accepts opaque copy and transfers the electrostatic latent image directly to the paper base. in this modification opaque copy is fed by a synchronously driven endless belt 182 of transparent or translucent woven plastic webbing or plastic sheet past a slit 134 where it is illuminated by suitable lamps 186. A tray 188 receives the processed copy after passage through the projection head. A lens 190 images the copy on electrophotographic drum 192 behind slit 1%. The drum is charged and exposed, the electrostatic latent image reaching a transfer station 1% comprising an endless belt Tf8 carried on pulleys 2'00. Print paper from a roll 202 is fed between the drum and belt 193 where it receives the electrostatic latent image. Feeding is accomplished through metering rollers 2M and feed rollers 2% in accordance with signals provided by a control system.

The control system for feeding the print paper includes a sensing head 208 which can consist, for example, of either a photocell for detecting the passage of the front edge of a piece of copy, or a sensitive switch actuated by passage of the front edge of the piece of copy. The resulting signal is passed through an amplifier or relay Zltl into a control box 212 which selectively times the operation of (l) solenoid 214 for controlling drive rollers 2 94, (2) solenoid 216 for controlling rollers 2G6, and (3) solenoid 218 which operated a paper cutting knife 2 20.

The operation of the control is as follows. When a piece of copy 1 3i) enters slit 18d sensing head 2103 re sponds, solenoids 23.4 and 21s are actuated, and rolls 20 4 begin to feed paper toward roll 2%. After the follow ing edge of copy E80 passes the slit sensing head 283 again responds, solenoid 214 is deenergized, and rollers 294 are stopped. Solenoid 2418 is then operated, cutting the paper sufficiently long to receive the complete trans ferred image with such additional border as is required. Rollers 2%, which may or may not have been stopped during the cutting operation, continue to feed the cut piece of paper past a charging station 2 2 2, and into the transf r station, after which solenoid 2116 is deenergized, thereby stopping rollers 2M, or permitting them to overrun if such is desirable. Belt 1% rops the piece of paper onto a second endless belt which is preferably of porous rubber or plastic construction and which carries the paper through a developing station 226 preferably of the powder cloud type. A pair of suction heads 23% serve to hold the paper against the belt as the latter enters the developing station and to entrain and remove any of the developer cloud which escapes between the lip of the station and the belt. The sheet is dropped from the lower end of belt 22 onto an endless conveyor belt 230 which carries the sheet under a fixing chamber 232 and discharges it into a receiving tray .234.

The transfer belts 5 6 and lid used in the modifications of P168. 4 and 5 respectively can be of solid cross section for most applications. It it sometimes desirable, however, to provide the transfer surface with a texture or pattern for the purpose of improving the rendition of half-tones, for improving the fill-in of large solid black areas in the copy, or for the otherwise breaking up the electrostatic latent image into a number of minute charge areas. In normal electrophotography large solid black areas do not fill in well with developer because of characteristics of electric fields. By breaking up the single charge at these large solid areas into a multiplicity of smaller ones the developer can produce a uniform. density in these areas.

Four modifications of belt surfaces are shown in FIGS. 8 to T1. IG. 8 shows a plastic or rubber belt body 25% provided with uniformly or randomly spaced fiat topped projections 252 the width of which may vary from 0.3 mm. to 0.03 mm. The tops of these projections may be from 1 to 0.1 mm. above the bottom of the depressed surface 25d between the projections. The depressed surface is provided with a conducting layer 256 of evaporated metal or metal foil. This belt is readily produced by heating the plastic surface, embossing it with a roller or die plate, coating the surface with evaporated alumimum, and removing the aluminum at the top of the projections by polishing against an abrasive surface. Alternatively a piece of adhesive-backed metal foil can be placed on the heated plastic surface, pressed with a patterned roller or die to obtain bonding and to simultaneously produce the projections, and the unwanted foil removed from the tops of the projections by abrasion or by roller coating the tops of the projections with an acid.

In the arrangement shown in FIG. 9 the plastic or rub ber base is embossed to produce a series of rounded projections 258 having dimensions similar to those of projections 2 52 of FIG. 8 and a radius of curvature between .0115 mm. and 1.5 mm.

FIG. '10 shows a belt having alternately raised insulating portions 260 and depressed conducting portions 262. The latter may be of rubber or plastic containing electrically conductive ingredients for lowering the resistivity of these portions. Such a belt may be made by studding a plain belt of low resistivity material with small beads or bits of high resistivity material and vulcanizing or polymerizing the two materials to each other.

In FIG. 11 a belt base 264, which may be of high or low conductivity flexible material or webbing, is covered with a layer of high resistivity material of spongelike or cellular construction and which may or may not contain low resistivity partiolels.

It is also possible to provide paper having surface characteristics generally similar to those of the belts shown in FIGS. 8 to 11 to thereby obtain the same advantages without requiring the use of a transfer belt as in the printers shown in FIGS. 6 and 7.

Obviously the trans-fer of the electrostatic latent image can be employed in eleetrophotographic cameras as well as printers. The rotating drum can be used in aerial stri cameras for example. Charges can of course be transferred from fiat electrop-hotographic plates onto intermediate electrostatic image blankets which can be developed and the powder image transferred to a suitable base on which it is fixed. Also, transfer of the electrostatic latent image from a flat plate directly onto the final base where it is developed and fixed is feasible.

I claim:

An electrophotographic printer comprising a rotating electrophotographic drum, charging means for sensitizing said drum, means for producing an image on said drum to form thereon an electrostatic image, a transfer belt in contact with said drum for receiving the electrostatic image therefrom, a developing station for developing said image on said belt into an image layer and a plurality of developed image transfer stations for successively transferring a proportion of the image layer to a layer of base material.

References Cited in the file of this patent UNITED STATES PATENTS 1,391,743 Lipsius Sept. 27, 1921 2,551,582 Carlson May 8, 1951 2,603,575 Schramm July 15, 1952 2,736,770 McNaney Feb. 28, 1956 2,833,648 Walkup May 6, 1958 2,895,847 Mayo July 21, 1959 3,002,434 Reuter Oct. 3, 1961 3,003,404 Metcalfe et al Oct. 10, 1961 3,040,704 Bliss June 26, 1962 3,059,614 Limberger Oct. 23, 1962 3,084,061 Hall Apr. 2, 1963 

